The statements in this section merely provide background information related to the present disclosure and do not constitute prior art. A semiconductor memory device is generally divided into a volatile memory device and a non-volatile memory device.
The volatile memory device offers fast read and write speeds but loses data stored in memory cells when power is removed. The non-volatile memory device has relatively slower read and write speeds but retains data even when a power supply is interrupted or blocked. Therefore, in order to store data that needs to be stored regardless of whether powered or not, the non-volatile memory device is employed. The non-volatile memory device includes a read only memory (ROM), a mask ROM (MROM), a programmable ROM (PROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a flash memory, a phase change random access memory (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), a ferroelectric RAM (FRAM), etc. The flash memory is divided into a NOR flash memory and a NAND flash memory.
The flash memory has two advantages. First, it freely programs and erases data, an advantage of a random access memory (RAM). Second, it retains data even when not powered, an advantage of the ROM. The flash memory is widely used as a storage medium for mobile electronic devices such as a digital camera, a personal digital assistant (PDA), an MP3 player, etc.
Recently, as the number of memory cells included in a string and the number of bits in data stored in a memory cell increase in a semiconductor memory device, the inventor(s) has noted that it has become necessary to carry out a program operation of a semiconductor memory device in an effective manner.